The present invention provides copolymers of hexafluoroisobutylene (HFIB) and vinyl esters (VE), especially vinyl acetate (VA), which can be prepared under homogeneous radical conditions. They have a 1:1 alternate microstructure over a wide range of monomer feed ratios. The HFIB-VA alternating copolymer is amorphous, having a glass transition temperature of around 50.degree. C.; it can be readily dissolved in various polar solvents such as ketones, dimethylformamide, and diglyme. The solutions can be used to make coatings and to cast films. These HFIB-VE copolymers can be hydrolyzed to form amorphous copolymers of HFIB and vinyl alcohol, or terpolymer of HFIB with VE and vinyl alcohol (HFIB-VOH copolymer and HFIB-VE-VOH terpolymer), which possess the desirable properties characteristic of fluoropolymers. They are soluble in many organic solvents, and strongly adherent to substrates.
There is a need for coating materials which have the superior properties of fluoropolymers--such as low refractive index and surface energy, excellent thermal and chemical resistance--and which at the same time meet the basic requirements for coatings, i.e. strong adhesion, hardness, toughness, abrasion resistance and liquid processability. Most known fluoropolymers do not not meet this combination of requirements; they do not dissolve easily in solvents for coating purposes, their adhesion to substrates is poor, and they are not as hard and abrasion-resistant as other conventional polymers such as acrylics or urethanes. The HFIB-based polymeric compositions of the present invention have the above-mentioned superior properties.
Vinyl esters have been previously copolymerized with certain reactive fluoroolefins such as tetrafluoroethylene, chlorotrifluoroethylene, and vinyl fluoride [M. Modena et al., Eur. Polym. J. 3 (1967), p.5; A. Korin et al J. Polym. Sci., Polym. Chem. Ed. 18 (1980), p.109].
An alternating copolymer of HFIB with vinylidene fluoride has been disclosed and is commercially available from Ausimont USA under the tradename CM-X [P. S. Minhas et al., Plastics Engineering, 3 1977, p.60; A. B. Robertson et al., SAMPE Tech. Conf. 18 (1986), p.490]. However, this copolymer is highly crystalline and is not known to dissolve in any solvent. A terpolymer containing 48% of HFIB, 44% of vinyl fluoride, and 10% of vinyl 4-hydroxybutyl ether has been recently disclosed [Europ. Pat. 150,725].
Among the various fluoroolefins, hexafluoroisobutylene [HFIB, 3,3,3-trifluoro-2-(trifluoromethyl)-prop-1-ene, hexafluoroisobutene, (CF.sub.3).sub.2 C.dbd.CH.sub.2 ] is relatively new and less studied. From a structural point of view, polymers containing HFIB are interesting since the presence of two bulky trifluoromethyl pendant groups should provide excellent stability and properties characteristic of fluorine-containing polymers, such as low surface tension and refractive index. Unfortunately, HFIB monomer does not homopolymerize, and no basis is known for predicting which monomers can be copolymerized with HFIB.